Effects of Sitagliptin in Individuals With Genetically Decreased DPP4

Inclusion Criteria: * Participant of the Penn Medicine Biobank who is willing to be recontacted to participate in future research. * Cases are defined as adults 18-70 years with likely decreased DPP4. * Controls are defined as adults who are matched to cases by: age, gender, race, BMI, hypertension status, diabetes status, renal function, and medication use that may affect outcomes of interest. Exclusion Criteria: * The study will exclude volunteers with any significant medical conditions that may interfere with study participation, data interpretation, or pose safety risk(s) to the subject. * Recent hospitalization or acute illness such as infection within the past two weeks * Pregnancy * Use of insulin * Use of a GLP-1 agonist or DPP4 inhibitor medication * Use of oral diabetes agents other than metformin unless matched with controls * Type 1 diabetes * Chronic steroid use or use within the last 30 days * Significant liver disease including liver enzymes \>3 x upper limit of normal range * Renal dysfunction defined as eGFR\< 50mL/min/1.73m2 * Significant cardiac disease such as heart transplantation * Significant gastrointestinal conditions that may interfere with drug absorption or GLP-1 release including bariatric surgery * Significant hematologic disease such as hematocrit \<35% * Use of chronic anticoagulation * Severe pulmonary disease * Severe neurologic or psychiatric disease * Inability to comprehend study procedures